BAGHDAD — A day after the United States withdrew its last combat troops, Iraq faced a dangerous political crisis Monday as the Shiite-dominated government ordered the arrest of the Sunni vice president, accusing him of running a death squad that assassinated police officers and government officials.

The sensational charges drew a worried response from Washington and brought Iraq’s tenuous partnership government to the edge of collapse. A major Sunni-backed political coalition said its ministers would walk off their jobs, leaving adrift agencies that handle Iraq’s finances, schools and agriculture.

The accusations against Vice President Tariq al-Hashimi also underlined fears that Iraq’s leaders may now be using the very institutions America has spent millions trying to strengthen — the police, the courts, the media — as a cudgel to batter their political enemies and consolidate power.

On Monday night, al-Hashimi was in the northern semiautonomous region of Kurdistan, beyond the reach of security forces controlled by Baghdad. It was unclear when — or if — he would return to Baghdad.

In Washington, where officials have been quietly celebrating the end of the war, Obama administration officials sounded alarmed about the arrest order for al-Hashimi.

“We are talking to all of the parties and expressed our concern regarding these developments,” said Tommy Vietor, the National Security Council spokesman. “We are urging all sides to work to resolve differences peacefully and through dialogue, in a manner consistent with the rule of law and the democratic political process.”

The breakdown in relations between Prime Minister Nouri al-Maliki and al-Hashimi and his Iraqiya Party arrived at an inopportune moment for the administration, coming so close to the troop withdrawal. U.S. officials have spent years trying to urge Iraq’s Shiite-dominated government to work with the country’s Sunni minority, and are wary of having things fall apart now.

President Barack Obama said last week, in remarks welcoming troops back to Fort Bragg, N.C., that Iraq’s future would now be “in the hands of the Iraqi people.” But having removed its combat troops, it was unclear whether the United States retained enough influence to limit sectarian tensions that some analysts say could drag the country back into the chaos and violence of past years and even split it along geographical lines.

The government made its case against al-Hashimi in a half-hour television broadcast that was as aggressively promoted as a prime-time special.

Not only was racial animus a likely factor when Charter Communications repeatedly rejected negotiations with Entertainment Studios, the TV programmer, but Charter's attempt to shield itself from allegations of bias using the First Amendment is also without merit, according to the U.S. Court of Appeals for the Ninth Circuit.